Maybe you can use the aggro section for something like the condition
@bytebite mentions, conditions are supposed to work there so it should look something like this:
AggroOn=1
AggroSize=1
Aggro1=Fading Memories|80|>||${Me.PctHPs} < 50 || (${Pulling} && ${Me.XTarget} > 3)
That might not be exactly right but, if you played around with something like that it might work? so aggro section set to on, and it will cast fading memories if you have 80% or better hate on the targeted mob and your hp are below 50% or your are pulling and you have greater than 3 xtargets? maybe start with Aggro1=Fading Memories|80|>||${Me.XTarget} > 3) to test it then add more to the condition?
The kissassist document says:
"Aggro1=WhatToDo|PctAggroToDoIt|<,<<,>|TargetFlag|Cond
AA/Disc/Item/Spell|% aggro|<,>,<< less than/greater than/double less than| Me/MA/Pet/Mob(Default) cast on Target.
use < to increase or maintain aggro
use > to decrease or avoid aggro
use << to check secondary aggro
Targetflag defaults to the targeted mob if left empty, or null. You may also use targetflag INC for incoming mobs, those further away than MeleeDistance. Targetflag Me, MA, and Pet are also accepted.
Aggro also evaluates Conditions."